When operating a mobile communications system, stability of the system is one of important elements. A failure leading to system operation halt must be prevented from occurring, a failure must be rapidly detected in case of occurrence of the failure, and recovery must be carried out in order to stably operate the system. Therefore, detection of a failure in a wireless base station and its diagnosing method are very important.
A transmitter and a receiver are mounted in the wireless base station. Detection of a failure in the transmitter of these devices can be relatively easily realized by divaricating a part of transmission main signals generated by the transmitter and monitoring the divaricated signal. On the other hand, detection of a failure in the receiver cannot be realized by just divaricating and monitoring a part of reception signals. That is because a power of the reception signal input to the receiver fluctuates every second in accordance with, e.g., an installation environment, the number of connected terminals, and others, and hence a threshold value that is required to judge whether a reception power value is normal or abnormal cannot be determined. Therefore, detection of a failure in the receiver is generally realized by inputting any known test signal to the receiver and monitoring a reception state of the receiver. A diagnosing method in the receiver is roughly classified into two methods depending on a generation method of this test signal.
One is a method of divaricating a part of output signals from the transmitter mounted in the same wireless base station apparatus and using the divaricated signal as a test signal, and it is called a loopback test (see, e.g., JP-A-2002-246978). The other is a method of mounting a test signal generator that outputs a test signal in the same wireless base station apparatus (see, e.g., JP-A-2001-127715). In both the methods, any known test signal must be input to the receiver to detect a failure in the receiver.